The overall objective of the proposed research is to understand the biology and regulation of a eukaryotic transposable element, the P element of Drosophila melanogaster. First, we will determine the number and structures of P element transcripts. Second, we will attempt to identify P element protein products. Third, we will analyze the functions of P element sequences and gene products using a combination of in vitro mutagenesis and germline transformation methods. Fourth, we will investigate the site specificity of P element insertion. Fifth, we will determine the structure of the hypermutable singed-weak allele and its derivatives. Sixth, we will investiage the mechanisms by which P element insertions disrupt gene function. Seventh, we will attempt to elucidate the mechanism by which P element transposition is apparently limited to the germline lineage. Eighth, we will look for extra-chromosomal circular forms of the P element and examine their potential role as mediators of cytotype or as intermediates in transposition. Finally, we will attempt to establish in vitro systems to facilitate the study of P element transcription and transposition mechanisms. Transposable genetic elements are well established as mediators of genetic change in both prokaryotes and eukaryotes. It is likely that they will be found in all species including man. They have already been detected in all organisms where the available genetic tools permit a careful screening - bacteria, yeast, plants and Drosophila. Transposable element-induced mutations account for a sizeable fraction of spontaneous mutations in these organisms and in yeast and Drosophila appear to account for the majority of cis-acting control mutations - mutations at a locus that affect its level or developmental timing of expression. Moreover, transposable elements appear to be the main inducers of chromosomal inversions, deletions and translocations in bacteria, yeast, plants and Drosophila.